Derivative Instruments - Summary of Gains and Losses on Derivative Instruments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments	$ 15,812	$ (3,263)	$ 40,620	$ (24,055)
Commodity Contract [Member] | Not Designated as Hedging Instrument [Member] | Gain (Loss) on Derivative Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments	$ 15,812	$ (3,263)	$ 40,620	$ (24,055)